How US Heat Waves Melted Greenland's Ice

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In a reversal of this year's extraordinary winter weather, Greenland suffered the wrath of North America's epic heat waves in 1889 and 2012, a new study reveals.

"Last winter in the eastern United States, people associated the cold with the behavior of the polar vortex," said lead study author William Neff, a fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder. "In fact the polar vortex can show two faces: a cold one or a warm one depending where you are. Last winter it showed its cold face to folks in the East. In the summer of 2012 it showed its warm face." [Video: 2 Extreme Melt Events 123 Years Apart]

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Though more than a century apart, both massive surface melts were triggered by soaring temperatures east of the Rocky Mountains, according to findings published yesterday (April 24) in the Journal of Geophysical Research: Atmospheres. It turns out that North America's furnacelike heat was funneled toward Greenland by an atmospheric river, a narrow, fast-flowing current of moist, warm air, Neff and his co-authors found. A warmer-than-average ocean off Greenland moistened the scorching air as it blasted north.

"Air was taken from the heat wave in the Midwest, moved to the east and then traveled over the ocean picking up moisture on the way to Greenland, where the warm air and clouds helped melt the ice over highest levels of Greenland," Neff told Live Science by email.

Both 1889 and 2012 saw record-shattering summer melts that liquefied nearly all of Greenland's icy surface. Ice core records suggest similar extreme melts hit about once a century between A.D. 750 and A.D. 1250, during a warmer North Atlantic climate known as the Medieval Warm Period.

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"These rare melt events on the highest elevations of Greenland require an unusual coincidence of factors," Neff said. "Understanding how they come together may help us better forecast the future of Greenland's ice and snow."

Earlier research had already identified the culprits in 2012's incredible thaw — warm air and thin clouds insulating the island like a blanket — but scientists were curious about what caused the remarkable weather pattern.